Tip leakage flow directionality control

ABSTRACT

A gas turbine engine according to an exemplary aspect of the present disclosure includes, among other things, an airfoil having a tip wall that joins outer spanwise ends of a suction sidewall and a pressure sidewall, a tip leakage control channel recessed into an outer surface of the tip wall, a tip leakage control vane integrally formed on the tip wall adjacent to the tip leakage control channel and an air seal radially outward of the tip wall and positioned to minimize leakage at the tip wall.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of pending U.S. patentapplication Ser. No. 13/540,752, filed Jul. 3, 2012.

BACKGROUND

The described subject matter relates generally to turbine engines andmore specifically to cooling turbine blades.

Turbine engines provide efficient, reliable power for a wide range ofapplications in aviation, transportation and industrial powergeneration. Individual compressor and turbine section(s) may besubdivided into a number of stages, formed of alternating rows of rotorblade and stator vane airfoils. Due to various operational constraints,rotor blades and stator vanes are prone to leakage of compressed gasesover their tips from a higher pressure surface to a lower pressuresurface. Several attempts have been made to reduce these flows, but theycannot be completely eliminated due to clearance requirements over theairfoil tips which account for variations in both thermal andcentrifugal growth of adjacent components.

SUMMARY

A gas turbine engine according to an exemplary aspect of the presentdisclosure includes, among other things, an airfoil having a tip wallthat joins outer spanwise ends of a suction sidewall and a pressuresidewall, a tip leakage control channel recessed into an outer surfaceof the tip wall, a tip leakage control vane integrally formed on the tipwall adjacent to the tip leakage control channel and an air sealradially outward of the tip wall and positioned to minimize leakage atthe tip wall.

In a further non-limiting embodiment of the foregoing gas turbineengine, the tip leakage control channel and the tip leakage control vaneare curved.

In a further non-limiting embodiment of either of the foregoing gasturbine engines, the air seal is a grooved blade outer air seal (BOAS).

In a further non-limiting embodiment of any of the foregoing gas turbineengines, the grooved BOAS includes a plurality projections that extendinwardly from a radially inner surface of the grooved BOAS.

In a further non-limiting embodiment of any of the foregoing gas turbineengines, a plurality of grooves extend between adjacent ones of theplurality of projections to define a circuitous flow path at theradially inner surface.

In a further non-limiting embodiment of any of the foregoing gas turbineengines, the tip leakage control channel includes an inlet and an outletrecessed into the outer surface of the tip wall, the inlet beginningproximate a junction of the pressure sidewall and the tip wall, and theoutlet terminating at a recessed portion of a junction of the tip walland the suction sidewall.

In a further non-limiting embodiment of any of the foregoing gas turbineengines, the tip leakage control vane projects radially outward in aspanwise direction from a tip floor of the tip wall, a leading portionof the tip leakage control vane beginning proximate a junction of thepressure sidewall and the tip wall, and a trailing portion of the tipleakage control vane terminating proximate a junction of the suctionsidewall and the tip wall.

In a further non-limiting embodiment of any of the foregoing gas turbineengines, a winglet extends from the tip leakage control vane at thesuction sidewall.

In a further non-limiting embodiment of any of the foregoing gas turbineengines, a channel cooling aperture has a curvature. The channel coolingaperture feeds airflow to the tip leakage control channel from aninternal cooling cavity.

In a further non-limiting embodiment of any of the foregoing gas turbineengines, the airfoil is a turbine airfoil.

A gas turbine engine according to an exemplary aspect of the presentdisclosure includes, among other things, an airfoil having a tip walland a grooved blade outer air seal (BOAS) positioned radially outward ofthe tip wall and configured to minimize clearances at the tip wall.

In a further non-limiting embodiment of the foregoing gas turbineengine, the grooved BOAS includes a plurality projections that extendinwardly from a radially inner surface of the grooved BOAS.

In a further non-limiting embodiment of either of the foregoing gasturbine engines, a plurality of grooves extend between adjacent ones ofthe plurality of projections to define a circuitous flow path at theradially inner surface.

In a further non-limiting embodiment of any of the foregoing gas turbineengines, the plurality of projections extend inwardly at an anglerelative to the radially inner surface.

In a further non-limiting embodiment of any of the foregoing gas turbineengines, a first projection of the plurality of projections extends at afirst angle and a second projection of the plurality of projectionsextends at a second, different angle.

In a further non-limiting embodiment of any of the foregoing gas turbineengines, the airfoil includes a tip leakage control channel recessedinto an outer surface of the tip wall.

A gas turbine engine method according to an exemplary aspect of thepresent disclosure includes, among other things, positioning a groovedblade outer air seal (BOAS) radially outward of a tip wall of an airfoilto define a circuitous flow path at a radially inner surface of thegrooved BOAS.

In a further non-limiting embodiment of the foregoing method, the methodincludes capturing a first portion of a leakage flow in a tip leakagecontrol channel formed into a radially outer surface of the tip wall.

In a further non-limiting embodiment of either of the foregoing methods,the method includes communicating a second portion of the leakage flowthrough the circuitous flow path.

In a further non-limiting embodiment of any of the foregoing methods,the method includes communicating a leakage flow along the circuitousflow path.

The embodiments, examples and alternatives of the preceding paragraphs,the claims, or the following descriptions and drawings including any oftheir various aspects or respective individual features, may be takenindependently or in any combination. Features described in connectionwith one embodiment are applicable to all embodiments, unless suchfeatures are incompatible.

The various features and advantages of this disclosure will becomeapparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts a cross-section of a turbofan gas turbineengine.

FIG. 2 shows a perspective of an exemplary gas turbine engine rotorblade.

FIG. 3A is a top plan view of the rotor blade shown in FIG. 2.

FIG. 3B is a partial cross-section of the rotor blade from FIG. 3A.

FIG. 3C is a graph showing relative pressures on opposing rotor bladesurfaces.

FIG. 4A depicts a vortex caused by leakage over the tip of the rotorblade.

FIG. 4B shows a second view of the vortex caused by leakage between thetip and an adjacent seal surface.

FIG. 5A is a magnified view of tip leakage control channels and vanes.

FIG. 5B shows angles of tip leakage control channels and vanes from FIG.5A.

FIG. 5C shows additional features to the tip leakage control channelsand vanes of FIG. 5A.

FIG. 6A is a top plan view of a first alternative rotor blade tip wallconfiguration.

FIG. 6B is a partial cross-section of the alternative rotor blade tipwall configuration shown in FIG. 6A.

FIG. 7A is a top plan view of a second alternative tip wallconfiguration.

FIG. 7B is a partial cross-section of the alternative tip wallconfiguration shown in FIG. 7A.

FIGS. 8A and 8B illustrate another tip wall configuration.

FIGS. 9A, 9B and 9C illustrate yet another tip wall configuration.

FIGS. 10A and 10B illustrate a vortex caused by leakage between a tipwall and an adjacent seal surface.

FIGS. 11A and 11B illustrate yet another tip wall configuration.

FIG. 12 illustrates another exemplary tip wall for an airfoil.

DETAILED DESCRIPTION

FIG. 1 is a cross-sectional view of gas turbine engine 10, including lowspool 12, low pressure compressor (LPC) 14, low pressure turbine (LPT)16, low pressure shaft 18, high spool 20, high pressure compressor (HPC)22, high pressure turbine (HPT) 24, rotor blades 25, high pressure shaft26, combustor 28, nacelle 30, propulsion fan 32, fan shaft 34, fan drivegear system 36, planetary gear 38, ring gear 40, sun gear 42, and fanexit guide vanes 44.

In the example two-spool, high bypass turbofan configuration, low spool12 includes low pressure compressor (LPC) 14 driven by low pressureturbine (LPT) 16 via low pressure shaft 18. High spool 20 includes highpressure compressor (HPC) 22 driven by high pressure turbine (HPT) 24via high pressure shaft 26. Low pressure shaft 18 and high pressureshaft 26 are mounted coaxially and rotate at different speeds. The powercore also includes combustor 28 arranged in flow series between thecompressor and turbine sections. HPT 24 and LPT 16 can each include atleast one stage of circumferentially distributed rotor blades 25. Moredetails of an example rotor blade 25 are described below.

Propulsion fan rotor 32 drives air through the bypass duct coaxiallyoriented between the engine core and nacelle 30. Fan rotor (or otherpropulsion stage) 32 can be directly or indirectly rotationally coupledto low pressure shaft 18. In advanced designs, fan drive gear system 36couples fan shaft 34 to low spool 12, with respective planetary, ring,and sun gear mechanisms 38, 40 and 42 providing independent fan speedcontrol for reduced noise and improved operating efficiency. In moreconventional turbofan designs, fan drive gear system 36 is omitted andfan 32 is driven directly as part of low spool 12. Fan exit guide vanes(FEGVs) 44 are disposed between nacelle 30 and the engine core to reduceswirl and improve thrust performance through the bypass duct. In morecompact engine designs, FEGV's may also be structural, providingcombined flow turning and load bearing capabilities.

It will be recognized from the remainder of the description that theinvention is by not limited to the example two-spool high bypassturbofan engine shown in FIG. 1. By way of further non-limitingexamples, fan rotor 32 may additionally or alternatively include anunducted rotor, with turbine engine 10 thereby operating as a turbopropor unducted turbofan engine. Alternatively, fan rotor 32 may be absent,leaving nacelle 30 covering only the engine core, with turbine engine 10thereby being configured as a turbojet or turboshaft engine. Thedescribed subject matter is also readily adaptable to other gas turbineengine components. While the working fluid is described here withrespect to a combustion gas turbine, it will be appreciated that thedescribed subject matter can be adapted to engines using other workingfluids like steam.

FIG. 2 is a perspective view of turbomachine rotor blade 25, and showsairfoil section 50, pressure sidewall 52, suction sidewall 54, base 56,leading edge 58, trailing edge 60, platform 62, root 64, tip wall 66,tip shelf 68, tip leakage control channels 70, and tip leakage controlvane 71.

Rotor blade 25 includes airfoil 50 defined in part by pressure sidewall52 (front) and suction sidewall 54 (back), each extending spanwise frombase 56, and chordwise between leading edge 58 and trailing edge 60.Base 56 can include platform 62 and root 64, which in this example ofrotating blade 25, secure airfoil 50 to a rotor disc (not shown). Tipwall 66 extends chordwise from leading edge 58 to trailing edge 60 tojoin respective outer spanwise ends of pressure sidewall 52 and suctionsidewall 54. Airfoil 50 can include one or more tip leakage controlelements on or around tip wall 66, such as tip shelf 68, tip leakagecontrol channel(s) 70, and tip leakage control vane(s) 71. While thisexample is shown as rotor blade 25, airfoil 50 can alternatively definean aerodynamic section of a cantilevered stator vane, with attendantmodifications made to the vane base for securing airfoil 50 to an outercircumferential casing.

In operation, pressurized gas flows generally chordwise along bothsidewalls 52, 54 from leading edge 58 to trailing edge 60. Airfoil 50 isprovided with one or more elements on or around tip wall 66, operatingin conjunction with adjacent elements of engine 10 to reduce tip leakagelosses. In this general example of blade 50, airfoil 25 includes tipshelf 68 at the junction of pressure sidewall 52 and tip wall 66. Itwill be recognized that in certain embodiments, tip shelf 68 may beomitted, leaving pressure sidewall 52 continuous up through its junctionwith tip wall 66. Tip wall 66 can also include at least one tip leakagecontrol channel 70 and/or leakage control vane 71, such as is shown inthe example embodiments below. With higher pressure differentialsfavored along the front-facing pressure sidewall 52, some of the higherpressure gas flowing along suction sidewall 54 tends to leak over tipwall 66. In traditional airfoil designs high pressure gradients from thepressure sidewall to the suction sidewall drives a leakage flow over thetip. This results in lost work extraction as the tangential momentum ofthe leakage flow is not changed by the airfoil, and higher aerodynamiclosses as the leakage flow is reintroduced into the main passage flow.Both of these effects result in reduced efficiency. Tip leakage controlchannel(s) 70 and tip leakage control vane(s) 71 reduce some of thenegative effects of this inevitable leakage flow.

FIG. 3A is a top plan view of a first example embodiment of airfoil 50,showing tip wall 66. FIG. 3B is an upstream-facing cross-section takenalong line 3B-3B. FIGS. 3A and 3B include pressure sidewall 52, suctionsidewall 54, leading edge 58, trailing edge 60, tip wall 66, tip shelf68, tip leakage control channels 70, tip leakage control vanes 71,control channel inlets 72, control channel outlets 74, tip outer surface76, tip rib 78, control vane leading portion 80, control vane trailingportion 81, control channel/vane sidewalls 82A, 82B, tip rib suctionside 84, control channel floors 86, internal cooling cavity 88, channelcooling apertures 90, tip shelf cooling apertures 92, and airfoilsidewall microcircuit 94.

In this first example embodiment, tip wall 66 includes at least onecurved tip leakage control channel 70 and at least one curved tipleakage control vane 71. More than one leakage control channel 70 can bedistributed across at least a chordwise portion of tip wall 66 extendingbetween airfoil leading edge 58 and airfoil trailing edge 60. Controlchannels 70 each include inlet 72 and outlet 74, which may be recessedinto or otherwise formed with radially outer surface 76 of tip wall 66.One or more corresponding spanwise tip leakage control vanes 71, can beformed with tip wall outer surface 76 between pairs of adjacent tipleakage control channels 70.

Channel inlets 72, generally disposed proximate the junction of pressuresidewall 52 and tip wall 66. Inlets 72 can be offset widthwise from ajunction in order to minimize effective tip clearance, and to block ortrip some of the leakage flow G_(L) across wall 66. The plurality ofchannel inlets 72 can be aligned along a chordwise path as shown. Incertain embodiments, channel inlets are aligned with tip rib 78, whichcan extend chordwise along at least a portion of the pressure side oftip wall 66 between airfoil leading edge 58 and airfoil trailing edge60. Tip rib 78 can be provided as part of outer surface 76 to clearancebetween radially adjacent engine components such as a casing, an airseal, or a rotor land (if configured as part of a stator vane). Controlvanes 71 may have a leading portion 80 defined in part bychordwise-adjacent channel inlets 72, and a trailing portion 81 definedin part by chordwise-adjacent channel outlets 74. In this example,channels 70 are defined by sidewalls 82A, 82B, which can alsorespectively serve as control vane pressure sidewall 82A and controlvane suction sidewall 82B. In certain embodiments, control vane leadingportion 80 is contiguous with suction side 84 of tip rib 78 to furtherreduce leakage flow while directing the remainder into and throughcontrol channels 70. Control vane trailing portions 81 may be contiguouswith suction sidewall 52 between channel outlets 74 terminating at arecessed portion of the junction of suction sidewall 52 and tip wall 66.

In this example, channel 70 has a box shaped cross-section, whereadjacent channel sidewalls 82A, 82B extend substantially perpendicularto flat channel floor 86. In this example, vanes 71 extend spanwise fromadjacent control channel floors 86 recessed into tip wall 66 from outersurface 76. In alternative embodiments, such as those shown in FIGS. 6Aand 6B, one or more vanes may extend spanwise from a lowered tip floorouter surface extending generally from airfoil leading edge 58 totrailing edge 60. It will be appreciated that one or more channels 70can additionally or alternatively have different cross-sections, andthose cross-sections can vary between inlet 72 and outlet 74. By way ofone non-limiting example, one or more channels 70 can have acontinuously curved sidewall to form a u-shaped cross-section. By way ofother non-limiting examples, one or more channels 70 can have angledfloors or sidewalls. In yet other examples, channel floor 86 can beomitted to form an upright v-shaped cross-section. Other irregularcross-sections are also possible for tailoring channels 70 and/or vanes71 to different tip leakage profiles.

In certain embodiments, airfoil 50 is an internally cooled turbineblade, and includes at least one internal cooling cavity 88. Coolingcavity 88 can be formed during investment casting of airfoil 50 usingone or more shaped casting cores. The cores may be made from ceramics,refractory metals, or a combination thereof. An example of a combinedceramic and refractory metal casting core is described in commonlyassigned U.S. Pat. No. 6,637,500 by Shah et al., which is hereinincorporated by reference in its entirety. Other casting core technologymay also be implemented.

One or more leakage control channels 70 can include at least one coolingaperture 90 in fluid communication with internal cavity 88 for coolingcontrol channel 70. While shown as a single round through hole drilledor cast into channel floor 86 proximate channel inlet 72, aperture 90may be one or more apertures 90, at least some of which can have analternative form or position tailored to the relative pressure profileover tip wall 66. Aperture 90 may, for example, additionally oralternatively discharge coolant into channel 70 from tip rib suctionside 84, and/or channel sidewalls 82A, 82B. Tip shelf 68 can alsoadditionally or alternatively include at least one pressure side coolingaperture 92 to direct coolant along the junction of pressure sidewall 52and tip wall 66. Apertures 92 thus may be diffusion holes or slots tocreate an effective wall of coolant along tip shelf 68 for impeding tipleakage. Apertures 92 can be in fluid communication with cooling cavity88, which may be the same cavity 88 feeding apertures 90, or it may be aseparate cooling cavity. In certain embodiments, pressure sidewall 52and suction sidewall 54 can include one or more microcircuit coolingcavities 94 formed separate from or contiguous with internal coolingcavity 88. Microcircuit(s) 94, which may be formed in pressure sidewall52 and/or suction sidewall 54 using at least one refractory metalcasting core, can optionally be in fluid communication with apertures 92or can alternatively feed coolant to dedicated apertures.

FIG. 3C is a graph of relative pressures around tip wall 66. FIG. 3Cgraphically shows the pressure relationship across tip wall 66 withvertical plotting of pressure ratio P_(s)/P_(t) at relative chordwisepositions x/x_(t). P_(s) is the localized static pressure and P_(t) isthe localized total pressure. For simplicity, the scale x/x_(t) ismeasured linearly along chordwise tip rib suction side 84, which alsodoubles in this example as an upstream wall of each channel inlet 72.Other relative scales may be used giving slightly different relativepressure readings, but the relative pressure profiles will besubstantially consistent across these different scales.

As is expected, pressure side (PS) and suction side (SS) readings ofP_(s)/P_(t) are equal when x/x_(t) is at point 0, corresponding toleading edge 58. The pressure differential ΔP increases then decreaseschordwise until being equal again when x/x_(t) reaches point 1,corresponding to trailing edge 60. The exact pressure relationship alongtip wall 66 will depend on operating conditions, sweep of the airfoil,relative curvatures of pressure sidewall 52 and suction sidewall 54,among other factors. It can be seen that in the example turbine airfoil50, there is a fairly large ΔP range around the midchord region of thetip. Around midchord, the PS pressure has not yet fallen off, while theSS pressure drops to a minimum before recovering close to trailing edge60. Here, the maximum pressure differential ΔP_(max) between pressureside flow G_(P) and suction side flow G_(S) occurs just forward ofmidchord.

As seen in FIG. 3A, tip wall 66 includes tip leakage control channels 70and control vanes 71 at various relative chordwise positions x/x_(t). Toillustrate operation of one such channel 70 disposed roughly midchordalong tip wall 66, FIG. 3C shows approximations of the relative pressuredifferentials ΔP₁ and ΔP₂, comparing leakage flow paths in aconventional blade tip versus a blade tip having at least one channel70. With a conventional tip, leakage flow G_(L) originating around pointP₁ of pressure sidewall 52 will take the shortest path over the tip walltoward point S₁ roughly perpendicular to pressure sidewall 52 at thatpoint. Leakage flow G_(L) thus collides roughly perpendicular withsuction flow G_(S) around point S₁. Since airfoil 50 is in relativerotational motion along with gas flows G_(P) and G_(S), and becausepressure side gas flow G_(P) is necessarily slower than G_(S), leakageflow G_(L) between points P₁ and S₁ has virtually zero relativechordwise momentum, and high circumferential momentum, compared tosubstantial chordwise momentum of suction flow G_(S).

In contrast, tip leakage control channel 70 captures a localized portionof leakage flow G_(L) at inlet 72, and redirects it through a curvedportion of channel 70 toward airfoil trailing edge 60. The redirectedflow is ejected from the channel, entering the suction side gas streamproximate point S₂, downstream of the normal point of entry S₁. Sincechannel 70 can be recessed below the outermost surface of tip wall 66,the flow enters the suction side gas stream below the junction ofsurface 76 and suction sidewall 54. In this example, P_(s)/P_(t) isactually greater at point S₂ than at point S₁, reducing the magnitude ofleakage based on a smaller pressure differential ΔP₂. By redirecting theentry point of leakage flow G_(L) downstream toward point S₂, channel 70(and control vane 71) also imparts/converts a portion of the momentuminto an increased chordwise component, which necessarily reduces theconflicting widthwise momentum component of the leakage flowperpendicular to suction side flow G_(S). This has two positive effectson the gas flows.

Redirecting leakage momentum downstream from point S₁ allows leakageflow G_(L) to more quickly integrate into G_(S), closer to suctionsidewall 54. Decreasing widthwise momentum and/or increasing thetangential momentum of leakage flow G_(L) entering suction side flowG_(S) reduces conflict and turbulence at the entry point(s) bypermitting less penetration of leakage flow G_(L) to into the main flowpath of suction gas flow G_(S). With a larger chordwise (tangential)momentum component aligned with flow G_(S), there also ends up beingless boundary flow disturbance of suction gas flow G_(S), reducing flowseparation around tip wall 66. All of these increase efficiency byreducing the size and strength of resulting tip leakage vortices asshown in FIGS. 4A and 4B.

FIG. 4A shows tip leakage vortices exiting channel 70 and beingintegrated into suction gas flow G_(S), and includes pressure sidewall52, suction sidewall 54, airfoil leading edge 58, airfoil trailing edge60, tip wall 66, tip shelf 68, and tip leakage control channels 70, andcontrol channel cooling apertures 90. FIG. 4B is a cross-section of tipwall 66 taken through channel 70 with air seal 96 radially adjacent tipwall 64 to minimize clearance at tip wall 66. Optional internal detailsof the blade and air seal 96, such as cavities and cooling apertureshave been omitted for clarity and to better illustrate the effects ofleakage control cavity 70.

Air seal 96 cooperates with tip wall 66 to minimize clearance, andoverall tip leakage therebetween. Air seal 96 can be any conventional orinventive blade outer air seal (BOAS) compatible with an unshroudedrotor blade. Air seal 96 may optionally include a sacrificial layer toreduce rubbing damage to tip rib 78, or more generally to tip wall 66,during maximum centrifugal and thermal expansion of airfoil 50 relativeto the surrounding casing (not shown) onto which air seal 96 is mounted.

As explained above with respect to FIG. 3C, large pressure differentialsacross tip wall 66 result in leakage flow G_(L) passing over tip shelf68 and tip rib 78 with substantial initial widthwise momentum. Channels70 and vanes 71 help capture a portion of that flow, and redirect itdownstream as it passes over tip wall 66, providing channel flow G_(C)with increased chordwise momentum compared to other leakage flow G_(L).The portion of leakage flow G_(L) flowing through channel 70 joins withsuction gas flow G_(S) at a higher pressure downstream location. Entryflow G_(E) results in vortex V when joining suction gas flow G_(S).However, position of vortex V is smaller and closer to suction sidewall54 than it would be absent leakage control channels 70 and vanes 71. Themagnitude of vortex V can also be reduced due to addition of chordwisemomentum to entry flow G_(E) from channels 70 and vanes 71.

FIG. 5A shows two adjacent tip leakage control channels 70 bounding anintermediate tip leakage control vane 71, and also includes pressuresidewall 52, suction sidewall 54, tip wall 66, tip shelf 68, tip leakagecontrol channels 70, tip leakage control vanes 71, control channelinlets 72, control channel outlets 74, tip outer surface 76, tip rib 78,vane leading portion 80, vane trailing portion 81, control channel/vanesidewalls 82A, 82B, tip rib suction side 84, and control channel floors86. Channel cooling apertures 90 and tip shelf cooling apertures 92 havebeen omitted for clarity.

As seen here, channel inlets 72 have first chordwise width W₁ proximatechannel inlet 72, and outlets have second chordwise width W₂ proximatechannel outlet 74. In certain embodiments, second chordwise width W₂proximate outlet 74 is equal to or less than first chordwise width W₁.In alternative embodiments, second width W₂ is greater than first widthW₁. Similarly control vane 71 includes leading chordwise thickness t₁proximate tip rib 78, and trailing chordwise thickness t₂ proximatesuction sidewall 54. In certain embodiments, trailing chordwisethickness t₂ is equal to or less than leading chordwise width t₁. Inalternative embodiments, thickness t₁ is greater than thickness t₂.Adjacent channels 70 can be separated by pitch P_(c), which is anaverage distance between the sidewalls 82A, 82B of adjacent channels 70.P_(c) is shown as average separation because the inlet and outlet widthsW₁, W₂ of individual channels 70 may vary in the same channel 70 as wellas between adjacent channels. In certain embodiments P_(c) is constantacross at least a chordwise portion of tip wall 66. Pitch P_(c) may varyelsewhere along tip wall 66 based on relative curvatures of channels 70and vanes 71, described below in FIG. 5B.

FIG. 5B shows the relative angles of channels 70 and vanes 71 shown inFIG. 5A. Channel inlet 72 forms channel entrance interior angle α₁relative to pressure sidewall 52. Channel outlet 74 forms channel exitinterior angle α₂ relative to suction sidewall 54. In certainembodiments, angle α₂ is less than or equal to α₁. The effectivecurvature radius of channel 70 is thus the same or greater than thelocal curvature radius of tip wall 66.

In certain of those embodiments, channel entrance angle α₁ is betweenabout 80° and about 95°. Channel entrance angle α₁ may be greater than90° when leakage flow G_(L) cascading over the upper region of pressuresidewall 52 is expected to have a substantial chordwise flow componentrelative to the motion of airfoil 50 at the leakage point. When leakageflow G_(L) is expected to have substantially zero chordwise momentumaround the leakage point, channel entrance angle α₁ may be less than orequal to about 90°. This may occur, for example, as a result of tipshelf 68 (and shelf cooling apertures 92) reducing net leakage flowG_(L).

Flow out of channel cooling apertures 90 (not shown in FIG. 5B) may alsoimpart a counteracting momentum component to channel flow G_(C) onceleakage flow G_(L) has entered inlet 72. In certain embodiments, channelexit angle α₂ can be less than about 90° which can impart additionalchordwise momentum to channel flow G_(C) exiting outlet 74. Similarly,control vane leading portion 80 forms leading interior angle β₁ relativeto pressure sidewall 52, and control vane trailing portion 81 formstrailing interior angle β₂ relative to suction sidewall 54. Angles β₁and β₂ are measured around the respective chordwise midpoint of vaneleading and trailing portions 80, 81. In certain embodiments, angle β₂is less than or equal to β₁.

FIG. 5B also illustrates another effect of tip leakage control channels70 and vanes 71. Since tip leakage flow typically enters channel 70approximate perpendicular to the local junction with pressure sidewall52, channel gas flow will tangentially strike sidewall 82A before beingredirected. This can cause initial flow turbulence directly abovechannel inlet 72, which introduces tip vortices into the clearance gapbetween tip wall 66 and air seal 96 (shown in FIG. 4B), blocking aportion of additional leakage flow G_(L) over tip wall 66. Theseclearance vortices can be further enhanced by coolant flow directedoutward from channel cooling apertures 92. In addition, tangentialcontact of channel flow G_(C) with channel/vane sidewall 82A imparts ameasure of thrust onto vane 71, allowing some work to be recovered fromleakage flow.

FIG. 5C is a side view of airfoil 50 with pressure sidewall 52, suctionsidewall 54, tip wall 66, tip shelf 68, tip leakage control channel 70,tip leakage control vane 71, leakage control channel inlet 72, leakagecontrol channel outlet 74, tip rib 78, leakage control vane leadingportion 80, leakage control vane trailing portion 81, leakage controlvane sidewall 82B, tip rib suction side wall 84, and leakage controlchannel floor 86.

FIG. 5C shows the radial dimensions of leakage control channel and vane70, 71. As in FIG. 4B, internal details of the blade such as cavitiesand cooling apertures have been omitted to show the remaining referencedimensions of leakage control channel 70 and vane 71. It can be seenhere that leakage control channel 70 can have first depth d₁ measuredfor example proximate inlet 72 and second depth d₂ proximate outlet 74.The depths are generally the respective distances that channel floor 86is recessed relative to an upper portion of tip wall 66. This upperportion may be the top of tip rib 78 and/or control vane 71, but incertain embodiments, first and second depths d₁, d₂ may be measured fromdifferent upper surface.

Similarly, a first height h₁ of leakage control vane 71 is measuredaround its leading portion 80, and a second height h₂ is measured aroundthe trailing portion 81. These heights h₁ and h₂ are typicallydetermined relative to channel floor 86. In certain embodiments,however, heights h₁ and h₂ can be determined relative to tip floor 76.

Depending on pressure differentials along a particular airfoil 50 (e.g.,as shown in FIG. 3C), dimensions, separation, and curvature of channels70 and vanes 71 may be adapted to optimize redirection of leakage flowwhile still maintaining adequate tip cooling and material strength.Dimensions of channels 70 and vanes 71 will also affect the practicaldimensions and angles that can be achieved. These relative dimensionsand pitches can be adapted optimize performance based on expected ormodeled pressure differentials at different locations around tip wall66. Relative curvatures can be defined first with dimensions resultingtherefrom, or relative dimensions may be defined with resultingcurvatures. The overall configuration of tip wall 66 can also bedetermined iteratively based on one or more constraints of the variouswidths, thicknesses, pitches, and angles.

For example, in locations where leakage is most likely, such asproximate midchord where pressure side pressures are highest, channels70 may have a wider inlet W₁. They can also be provided with a narroweroutlet width W₂ relative to W₁, which can increase the pressure and exitvelocity of leakage flow G_(L) entering the suction gas stream G_(S). Inother embodiments, at locations with lower relative suction sidepressures, W₂ may be the same as or even greater than W₁ in order tomore closely match the entry pressure and velocity. Further, therelative and absolute pressures, along with available tip wall surfacearea, will also determine the pitch P_(C) of channels 70. As before, themidchord region of tip wall 66 may have smaller pitch values P_(C). Itwill be recognized that widths W₁ will generally vary inversely withthickness t₁ and vice versa. Similarly, widths W₂ generally varyinversely with thickness t₂ and vice versa. As also explained below,channel floor 86 may be sloped such that d₂ is less than d₁.

FIG. 6A shows tip wall 166, which also includes pressure sidewall 52,suction sidewall 54, airfoil leading edge 58, airfoil trailing edge 60,tip shelf 168, tip leakage control channel 170, tip leakage controlvanes 171, control channel inlet 172, control channel outlets 174, tipfloor 176, tip rib 178, control vane leading portions 180, control vanetrailing portions 181, control channel/vane sidewalls 182A, 182B, tiprib suction side 184, control channel floor 186, channel coolingaperture 190, tip shelf cooling apertures 192, and airfoil sidewallmicrocircuit 194. FIG. 6B is a cross-section taken across line 6B-6B ofFIG. 6A.

Tip wall 166 is a first alternative embodiment of tip wall 66 describedabove. Similar to FIG. 2, pressure sidewall 52 and sidewall 54 eachextend spanwise from airfoil base 56 between leading edge 58 andtrailing edge 60. Airfoil 50 also includes tip wall 166 extendingchordwise from leading edge 58 to trailing edge 60. In this firstexample alternative embodiment, at least one curved tip leakage controlvane 171 projects radially outward in a spanwise direction from tip wall166. Control vanes 171 each include leading vane portion 180 andtrailing portion 181 between adjacent sidewalls 182A, 182B. Control vaneleading portion 180 begins proximate a junction of airfoil pressuresidewall 52 and tip wall 166. Control vane trailing portion 181terminates proximate a junction of airfoil suction sidewall 54 and tipwall 166.

In this first alternative embodiment, rather than having channelsrecessed into a tip floor as shown in FIGS. 3A and 3B, vanes 171 extendradially outward from a lower tip floor 176 extending at least partwaybetween airfoil leading edge 58 and trailing edge 60. More than oneleakage control vane 171 can be distributed chordwise across at least aportion of tip floor 176. A corresponding curved tip leakage controlchannel 170 can be defined at least in part by adjacent ones of theplurality of tip leakage control vanes 171. As above, channel inlet 172can be defined by adjacent control vane leading portions 180, andchannel outlet 174 can be defined by adjacent control vane trailingportions 181.

Tip rib 178 can also project spanwise from at least a chordwise portionof tip wall 166. In certain embodiments, tip rib 178 can extend at leastpartway between airfoil leading edge 58 and airfoil trailing edge 60along pressure side of tip wall 166, outward from tip floor 176. Incertain embodiments, such as is shown in FIG. 6A, of the control vaneleading portion 196 can be contiguous with tip rib suction side surface184. Tip shelf 168 with cooling apertures 192 (in fluid communicationwith internal cooling cavity 188 and/or microcircuits 194) can berecessed into a pressure side surface of tip rib 178. Alternatively, thepressure side surface of tip rib 178 can be an extension of pressuresidewall 52.

Similar to the illustrations shown in FIGS. 5A and 5B, control vane 171can have leading portion 180 forming leading interior angle β₁ relativeto pressure sidewall 52, and vane trailing portion forming interiorangle β₂ relative to suction sidewall 54. In certain embodiments, angleβ₂ can be less than or equal to β₁, which increases the chordwisecomponent of leakage flow to reduce vortices and enhances work recoveryfrom the captured leakage flow as described above with respect to FIGS.5A and 5B.

FIG. 7A shows tip wall 266, which also includes pressure sidewall 52,suction sidewall 54, airfoil leading edge 58, airfoil trailing edge 60,tip shelf 268, ramped tip leakage control channel 270, tip leakagecontrol vanes 271, control channel inlets 272, control channel outlets274, tip floor 276, tip rib 278, control vane leading portions 280,control vane trailing portions 281, control channel/vane sidewalls 282A,282B, tip rib suction side 284, ramped control channel floor 286,channel cooling aperture 290, tip shelf cooling apertures 292, andairfoil sidewall microcircuit 294. FIG. 6B is a cross-section takenacross line 6B-6B of FIG. 6A.

Tip wall 266 is a second alternative embodiment of tip wall 66 describedabove. Similar to FIG. 2, pressure sidewall 52 and sidewall 54 eachextend spanwise from airfoil base 56 between leading edge 58 andtrailing edge 60. Airfoil 50 also includes tip wall 266 extendingchordwise from leading edge 58 to trailing edge 60. In this secondexample alternative embodiment, tip shelf 266 includes at least onecurved and ramped tip leakage control channel 270.

In this second example alternative embodiment, leakage control channelfloor 286 is ramped upward, in contrast to the substantially flatchannel floor 86 shown in FIGS. 3A and 3B. Thus, control channel 270 isshallower at the suction side exit than at the pressure side inlet. As aresult, leakage flow G_(L) is provided with increased pressure and exitvelocity is decreased, allowing for more uniform leakage flow enteringsuction gas stream G_(S).

Leakage flow can be further controlled by widening control channeloutlets 274. As was shown in FIGS. 5A and 5B, leakage control channelshave an inlet width W₁ that may be the same as or differ from outletwidth W₂. In certain embodiments, including but not limited to thesecond alternative example embodiment of FIGS. 7A and 7B, outlet widthW₂ is greater than inlet width W₁ so as to further improve uniformity ofthe leakage flow entering suction gas stream G_(S). In certain of thoseembodiments, outlet width W₂ is approximately equal to the pitch P_(C)between adjacent control channels (see FIG. 5A). In such embodiments, asoutlet width W₂ approaches the local channel pitch P_(C), the trailingchordwise thickness t₂ of adjacent leakage control vanes 271 will beless than leading control vane thickness t₁ and will approach zero atthe junction of suction sidewall 54 and tip wall 266. These shapes alsocontribute to reduced flow separation and tip vortices adjacent leakagecontrol vanes 271.

FIGS. 8A and 8B illustrate a tip wall 366 of an airfoil 50. The tip wall366 is another alternative embodiment of the tip wall 66 describedabove.

The tip wall 366 includes a pressure sidewall 352, a suction sidewall354, a tip shelf 368, a tip leakage control channel 370 and a tipleakage control vane 371. The tip leakage control channel 370 includesan inlet 372, an outlet 374, and a control channel floor 386. A tip rib378 includes a tip rib suction side 384 that establishes an endwall nearthe inlet 372 of the tip leakage control channel 370. The controlchannel floor 386 of the tip leakage control channel 370 extends axiallybetween tip leakage control vane sidewalls 382A, 382B (only sidewall382B shown in FIG. 8A).

In this embodiment, a plurality of radiused walls 369 are formed on theinner diameter corners of each tip leakage control vane 371. Forexample, a radiused wall 369 may connect the tip rib suction side 384 tothe control channel floor 386 of the tip leakage control channel 370.The vane sidewalls 382A and 382B may also be connected to the controlchannel floor 386 via radiused walls 369 (best shown in FIG. 8B).

Among other benefits, the radiused walls 369 provide smooth surfaces forairflow to flow across as the airflow circulates through the tip leakagecontrol channels 370. The radiused walls 369 may additionally reduce thepotential for cracking at sharp corners of the tip wall 366.

The radiused walls 369 may include any radius. The radius may depend ondesign specific parameters, including but not limited to the coolingrequirements of the airfoil 50.

Other portions of the airfoil 50 may additionally or alternativelyinclude radiused walls 369. For example, as best shown in FIG. 8A, acorner 367 defined between a sidewall 361 and an endwall 363 of acooling cavity 388 formed inside the airfoil 50 may include a radiusedwall 369. This positioning of the radiused wall 369 may enable improvedflow of airflow into a channel cooling aperture 390 that feeds the tipleakage control channel 370 from the cooling cavity 388.

The locations of the radiused walls 369 shown in FIGS. 8A and 8B areintended as non-limiting. It should be appreciated that other locationsof the tip wall 366 could benefit from radiused walls 369. In addition,the use of radiused walls 369 may be combined with any other featuredescribed in this disclosure without departing from the scope of thedisclosure.

FIGS. 9A, 9B and 9C illustrate yet another embodiment of a tip wall 466of an airfoil 50. The airfoil 50 includes a pressure sidewall 452, asuction sidewall 454, an airfoil leading edge 458, an airfoil trailingedge 460, a tip wall 466, a tip shelf 468, and tip leakage controlchannels 470 dispersed between tip leakage control vanes 471. In oneembodiment, the tip leakage control channels 470 and tip leakage controlvanes 471 are curved.

In this embodiment, the tip wall 466 includes a winglet 401 that extendsfrom the suction sidewall 454 of the airfoil 50. In one non-limitingembodiment, the winglet 401 is formed at a junction between the suctionsidewall 454 and the tip leakage control vane 471. The winglets 401 canreduce the inducement of a vortex V that is results from a leakage flowG_(L) joining suction gas flow G_(S) near the suction sidewall 454.

In a first embodiment, the winglet 401 may span the entire distancebetween the leading edge 458 and the trailing edge 460 of the airfoil 50(see FIG. 9A). The winglet 401 is located adjacent to the suctionsidewall 454, in one embodiment.

In an alternative embodiment, each tip leakage control vane 471 includesa winglet 401 (see FIG. 9B). Each winglet 401 represents a discreteportion of the tip wall 466 that extends from each tip leakage controlvane 471. In other words, the winglets 401 may be localized features ofeach tip leakage control vane 471. The winglets 401 may be formed on thecontrol vane trailing portions 481 of the tip leakage control vanes 471.

The winglets(s) 401 may be used either alone or in combination with anyother tip wall feature described in this disclosure. By way of onenon-limiting example, the winglet 401 could be used in combination withthe tip wall 366 described above that includes one or more radiusedwalls 369.

FIGS. 10A and 10B illustrate yet another tip wall 566 of an airfoil 50.In this embodiment, the tip wall 566 is positioned relative to an airseal 596. The air seal 596 is positioned radially outward of the tipwall 566 to minimize clearances at the tip wall 566.

In one embodiment, the air seal 596 is a grooved BOAS that includes aplurality of projections 505 that extend inwardly from a radially innersurface 507 of the air seal 596. Grooves 509 extend between adjacentprojections 505 and define pockets for circulating leakage airflow alonga circuitous path. The “grooved” air seal 596 cooperates with the tipwall 566 to minimize clearances and overall tip leakage that may occurbetween the airfoil 50 and the air seal 596. Although shown angled inthis embodiment, the projections 505 and/or grooves 509 can be at anyangle of 90° or less. In addition, each projection 505/groove 509 maynot necessarily extend at the same angle. Furthermore, although theprojections 505/grooves 509 are shown positioned axially relative to oneanother in FIGS. 10A and 10B, these features could be circumferentiallyarranged. Other arrangements are also contemplated.

Referring to FIG. 10B, the tip wall 566 could optionally include one ormore winglets 501 (similar to those described in FIGS. 9A, 9B and 9C).The combination of a “grooved” air seal 596 and the winglets 501desensitizes the mechanical tip clearance of the tip wall 566. Other tipwall embodiments could alternatively be used in combination with agrooved BOAS.

FIGS. 11A and 11B illustrate additional embodiments of a tip wall 666.The tip wall 666 can include a pressure sidewall 652, a suction sidewall654, a tip shelf 668, a tip leakage control channel 670, a tip leakagecontrol vane 671, a control channel floor 686, an internal coolingcavity 688, a channel cooling aperture 690, and, optionally, a tip shelfcooling aperture 692 (shown omitted in FIG. 11B).

In this embodiment, the channel cooling aperture 690 includes acurvature 615. The curvature 615 directs airflow at a specific angleinto the tip leakage control channel 670 from the internal coolingcavity 688 located inside of the airfoil 50. In the embodiment shown inFIG. 11A, the channel cooling aperture 690 opens through the controlchannel floor 686 and divides the floor 686 into a stepped surface 617in order to accommodate the curvature 615 of the channel coolingaperture 690. The stepped surface 617 includes a first surface 619 thatis elevated relative to a second surface 621. The first surface 619extends from a tip rib suction side 684 of a tip rib 678, while thesecond surface 621 extends from the suction sidewall 654.

Referring to FIG. 11B, a channel cooling aperture 690-2 with curvature615-2 extends further into the tip leakage control channel 670 than theFIG. 11A embodiment. In one embodiment, the channel cooling aperture690-2 extends to an outlet 674 of the tip leakage control channel 670and is used in conjunction with a winglet 601 that extends from the tipleakage control vane 671 at the suction sidewall 654 of the tip wall666. The channel cooling apertures 690, 690-2 may be individual holes orcould be continuations of the internal cooling cavity 688, such as aslot, etc.

In another embodiment, a tip outer surface 676 of the tip wall 666includes a first surface 623 and an angled surface 625. The firstsurface 623 extends from the tip shelf 668 to the tip rib suction side684 and may be at least partially flat. The angled surface 625 mayextend radially inwardly from the first surface 623 into the tip leakagecontrol channel 670. The angled surface 625 establishes a relativelysmooth surface for directing airflow into and through the tip leakagecontrol channel 670 from a location outside of the airfoil 50.

The angled surface 625 may be utilized in a tip wall configurationeither alone or in combination with any other features. This disclosureis not limited to the exact configuration shown in FIG. 11B, whichshows, as a non-limiting embodiment, a tip wall that includes acombination of features including the angled surface 625, winglet 601and channel cooling aperture 690 with curvature 615.

FIG. 12 illustrates yet another non-limiting embodiment of a tip wall766. The exemplary tip wall 766 can include a pressure sidewall 752, asuction sidewall 754, a tip shelf 768, a tip leakage control channel770, a tip leakage control vane 771, an internal cooling cavity 788, andone or more airfoil sidewall microcircuits 794 (or skin cores/radialflow passage skin cores).

In this embodiment, the airfoil sidewall microcircuit 794 feeds airflowF directly into the tip leakage control channel 770. The airfoilsidewall microcircuit 794 includes curved portions 799 that alter a flowdirection of the airflow F within the airfoil sidewall microcircuit 794.In one embodiment, one of the curved portions 799 is located near aninlet 772 of the tip leakage control channel 770. In this way, theairflow F is aligned in the direction of the tip leakage control channel770 as it is communicated into the inlet 772. Put another way, theairflow F is communicated generally parallel to a control channel floor786 of the tip leakage control channel 770 by incorporating the curvedportions 799 into the airfoil sidewall microcircuit 794.

Although the different non-limiting embodiments are illustrated ashaving specific components, the embodiments of this disclosure are notlimited to those particular combinations. It is possible to use someother components or features from any of the non-limiting embodiments incombination with features or components from any of the othernon-limiting embodiments.

It should be understood that like reference numerals identifycorresponding or similar elements through the several drawings. Itshould also be understood that although a particular componentarrangement is disclosed and illustrated in these exemplary embodiments,other arrangements can also benefit from the teachings of thisdisclosure.

The foregoing description shall be interpreted as illustrative and notin any limiting sense. A worker of ordinary skill in the art wouldunderstand that certain modifications could come within the scope ofthis disclosure. For these reasons, the following claims should bestudied to determine the true scope and content of this disclosure.

What is claimed is:
 1. A gas turbine engine, comprising: an airfoilhaving a tip wall that joins outer spanwise ends of a suction sidewalland a pressure sidewall; a tip leakage control channel recessed into anouter surface of said tip wall; a tip leakage control vane integrallyformed on said tip wall adjacent to said tip leakage control channel;and an air seal radially outward of said tip wall and positioned tominimize leakage at said tip wall.
 2. The gas turbine engine as recitedin claim 1, wherein said tip leakage control channel and said tipleakage control vane are curved.
 3. The gas turbine engine as recited inclaim 1, wherein said air seal is a grooved blade outer air seal (BOAS).4. The gas turbine engine as recited in claim 3, wherein said groovedBOAS includes a plurality projections that extend inwardly from aradially inner surface of said grooved BOAS.
 5. The gas turbine engineas recited in claim 4, comprising a plurality of grooves that extendbetween adjacent ones of said plurality of projections to define acircuitous flow path at said radially inner surface.
 6. The gas turbineengine as recited in claim 1, wherein said tip leakage control channelincludes an inlet and an outlet recessed into said outer surface of saidtip wall, said inlet beginning proximate a junction of said pressuresidewall and said tip wall, and said outlet terminating at a recessedportion of a junction of said tip wall and said suction sidewall.
 7. Thegas turbine engine as recited in claim 1, wherein said tip leakagecontrol vane projects radially outward in a spanwise direction from atip floor of said tip wall, a leading portion of said tip leakagecontrol vane beginning proximate a junction of said pressure sidewalland said tip wall, and a trailing portion of said tip leakage controlvane terminating proximate a junction of said suction sidewall and saidtip wall.
 8. The gas turbine engine as recited in claim 1, comprising awinglet that extends from said tip leakage control vane at said suctionsidewall.
 9. The gas turbine engine as recited in claim 1, comprising achannel cooling aperture having a curvature, wherein said channelcooling aperture feeds airflow to said tip leakage control channel froman internal cooling cavity.
 10. The gas turbine engine as recited inclaim 1, wherein said airfoil is a turbine airfoil.
 11. A gas turbineengine, comprising: an airfoil having a tip wall; and a grooved bladeouter air seal (BOAS) positioned radially outward of said tip wall andconfigured to minimize clearances at said tip wall.
 12. The gas turbineengine as recited in claim 11, wherein said grooved BOAS includes aplurality projections that extend inwardly from a radially inner surfaceof said grooved BOAS.
 13. The gas turbine engine as recited in claim 12,comprising a plurality of grooves that extend between adjacent ones ofsaid plurality of projections to define a circuitous flow path at saidradially inner surface.
 14. The gas turbine engine as recited in claim12, wherein said plurality of projections extend inwardly at an anglerelative to the radially inner surface.
 15. The gas turbine engine asrecited in claim 14, wherein a first projection of said plurality ofprojections extends at a first angle and a second projection of saidplurality of projections extends at a second, different angle.
 16. Thegas turbine engine as recited in claim 11, wherein said airfoil includesa tip leakage control channel recessed into an outer surface of said tipwall.
 17. A gas turbine engine method, comprising: positioning a groovedblade outer air seal (BOAS) radially outward of a tip wall of an airfoilto define a circuitous flow path at a radially inner surface of thegrooved BOAS.
 18. The method as recited in claim 17, comprisingcapturing a first portion of a leakage flow in a tip leakage controlchannel formed into a radially outer surface of the tip wall.
 19. Themethod as recited in claim 18, comprising communicating a second portionof the leakage flow through the circuitous flow path.
 20. The method asrecited in claim 17, comprising communicating a leakage flow along thecircuitous flow path.